1. Field of the Invention
This invention relates to siloxane elastomer compositions containing manganous oxide.
2. Description of the Prior Art
Electrical insulation based on siloxane elastomers has been well accepted due to the inherent heat stability of the polydiorganosiloxane used. Nevertheless, much work has been done to improve the characteristics of siloxane elastomers to make them even more suitable as electrical insulation. Additives have been discovered to improve many of the properties of siloxane elastomers including heat stability and flame retardancy.
In U.S. Pat. No. 3,137,670, Maneri discloses the use of certain isolated metallic oxides and hydroxides as excellent heat stability additives in place of the iron oxide and rare earth metal oxides already known. One of the compounds listed as useful is manganese dioxide.
In U.S. Pat. No. 3,162,722, Bartos discloses new electrical insulation components and a method for employing the components together to give improved insulation. One of the components is a diorganopolysiloxane containing a metallic oxide filler. The metallic oxide filler consists of oxides of metals ranging from aluminum to bismuth in the periodic table of elements except potassium, calcium, rubidium, strontium, cesium, and barium. The filler is generally from 20 to 400 parts, preferably 50 to about 200 parts per 100 parts of diorganopolysiloxane. Less than 20 parts can be added, but its effect will be very small. The preferred fillers are titanium dioxide, zinc oxide, and ferric oxide. Bartos teaches that Mn.sub.2 O.sub.3 is a suitable metallic oxide filler.
In U.S. Pat. No. 3,936,476, Itoh et al. disclose silicone compositions containing platinum containing material and manganese carbonate. Finished products prepared by molding the compositions exhibit particularly excellent flameproofing and improved degrees of permanent strain caused by stress. The composition contains from about 5 to about 100 parts by weight of manganese carbonate having a particle size of from about 1 micrometer to about 50 micrometers. Itoh et al. teach that the finely divided manganese carbonate, in cooperation with platinum-containing material, imparts excellent flame-retardant and self-extinguishing properties to the resulting silicone elastomers due to its function of generating CO.sub.2 gas under heat as well as its catalytic function. Other carbonates, calcium carbonate, zinc carbonate, and the like, impart no improved self-extinguishing effects to the resulting elastomers.
In U.S. Pat. No. 3,635,874, Laur et al. disclose a flame-retardant silicone composition consisting essentially of 100 parts of polydiorganosiloxane gum, reinforcing silica filler, organic peroxide, platinum, and fume TiO.sub.2 having an average particle diameter of less than 0.10 micron. Additional flame-retardant properties are observed by the addition of sulphur free carbon black.